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Common Shares - The effects of the Corporation's purchase and cancellation of the common shares (Details) $ / shares in Units, $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 CAD ($) $ / shares shares | Dec. 31, 2019 CAD ($) $ / shares shares | Dec. 31, 2018 CAD ($) $ / shares shares
Disclosure of classes of share capital [line items] |  |  |
Deficit | $ (1,826) | $ (1,455) |
Number of shares issued and fully paid that were not cancelled due to timing differences between the transaction date and settlement date | shares | 456,200 | 189,900 |
NCIB Program |  |  |
Disclosure of classes of share capital [line items] |  |  |
Number of shares issued and fully paid | shares | 7,352,600 | 7,716,300 | 3,264,500
Par value per share | $ / shares | $ 8.33 | $ 8.80 | $ 7.02
Issued capital | $ 61 | $ 68 | $ 23
Weighted average share price | 79 | 83 |
Deficit | $ 18 | $ 15 |
Par value per share | $ / shares | $ 8.33 | $ 8.80 | $ 7.02
Common shares |  |  |
Disclosure of classes of share capital [line items] |  |  |
Issued capital | $ 2,896 | $ 2,978 | $ 3,059

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